The present invention generally relates to parking brakes and, more particularly, to electrically powered parking brakes.
Almost all vehicles have a parking brake mechanism, and most of these vehicles have a hand or foot activated lever for manually actuating the parking brake mechanism. Typically, these levers are attached to a cable that causes displacement of the cable and operation of the attached parking brake mechanism. There is a need to provide an electrically actuated cable mechanism that operates reliably with a minimum number of parts and has a low cost, so that manually actuated mechanism may be replaced or easily selectively replaced.
It is known in the art to provide electric-motor driven brake systems. For example, see U.S. Pat. Nos. 4,281,736, 4,561,527, 4,629,043, 4,795,002, 4,865,165, 5,180,038, 5,485,764, 5,542,513, and 5,590,744 which each disclose an electric motor-driven brake system, the disclosures of which are expressly incorporated herein in their entirety by reference.
While these electric-motor driven brake systems may adequately actuate the brake mechanisms with varying degrees of success, they are inefficient, typically can be used in conjunction with only one type of cable system, must be mounted within the vehicle, have relatively large package sizes and utilize a large number of components, they are relatively heavy, and cannot be operated when the system is not powered. Accordingly, there is a need in the art for an improved electric parking brake assembly which has improved efficiency, can be used with conventional cable systems or conduit reaction cable systems, can be mounted outside the vehicle, has a relative small package size, has a relatively small number of components, is relatively light weight, and can be manually actuated.
The present invention provides an electric parking brake for a motor vehicle which overcomes at least some of the above-noted problems of the related art. According to the present invention, an electric brake assembly for tensioning a brake cable attached to a brake such that tensioning of the brake cable affects application of the brake and untensioning of the brake cable affects release of the brake comprises, in combination, an electric motor having an output shaft, a control module coupled to the electric motor for controlling the electric motor, and a transmission coupling a threaded lead screw to the output shaft of the electric motor. The assembly further comprises a drive nut having a lead screw bore threadably receiving the lead screw therein and having a cable attachment for attaching the brake cable to the drive nut. The cable attachment has a central axis offset from a central axis of the lead screw. The control module controls the electric motor such that rotation of the output shaft causes motion of the transmission and rotation of the lead screw, rotation of the lead screw causes linear motion of the drive nut, and linear motion of the drive nut causes tensioning and untensioning of the brake cable.
According to another aspect of the present invention, an electric brake assembly for tensioning a brake cable attached to a brake such that tensioning of the brake cable affects application of the brake and untensioning of the brake cable affects release of the brake comprises, in combination, an electric motor having an output shaft, a control module coupled to the electric motor for controlling the electric motor, and a transmission coupling a threaded lead screw to the output shaft of the electric motor. The assembly further comprises an elongate guide shaft substantially parallel to and spaced apart from the lead screw, and a drive nut. The drive nut has a lead screw bore threadably receiving the lead screw therein and a guide shaft bore slidingly receiving the elongate guide shaft therein. The drive nut also has a cable attachment for attaching the brake cable to the drive nut. The control module controls the electric motor such that rotation of the output shaft causes motion of the transmission and rotation of the lead screw, rotation of the lead screw causes linear motion of the drive nut along the lead screw and the guide shaft, and linear motion of the drive nut causes tensioning and untensioning of the brake cable.
According to yet another aspect of the present invention, an electric brake assembly for tensioning a brake cable attached to a brake such that tensioning of the brake cable affects application of the brake and untensioning of the brake cable affects release of the brake comprises, in combination, an electric motor having an output shaft, a control module coupled to the electric motor for controlling the electric motor, and a transmission coupling a threaded lead screw to the output shaft of the electric motor. The transmission comprises a gear train having a plurality of helical gears and the lead screw and the output shaft are substantially coaxial. The assembly further comprises a drive nut having a lead screw bore threadably receiving the lead screw therein and having a cable attachment for attaching the brake cable to the drive nut. The control module controls the electric motor such that rotation of the output shaft causes motion of the transmission and rotation of the lead screw, rotation of the lead screw causes linear motion of the drive nut, and linear motion of the drive nut causes tensioning and untensioning of the brake cable.
According to even yet another aspect of the present invention, an electric brake assembly for tensioning a brake cable attached to a brake such that tensioning of the brake cable affects application of the brake and untensioning of the brake cable affects release of the brake comprises, in combination, an electric motor having an output shaft, a control module coupled to the electric motor for controlling the electric motor, a transmission coupling a threaded lead screw to the output shaft of the electric motor, and a manual override device operatively connected to the lead screw. The assembly further comprises a drive nut having a lead screw bore threadably receiving the lead screw therein and having a cable attachment for attaching the brake cable to the drive nut. The control module selectively controls the electric motor such that rotation of the output shaft causes motion of the transmission and rotation of the lead screw, rotation of the lead screw causes linear motion of the drive nut, and linear motion of the drive nut causes tensioning and untensioning of the brake cable. The manual override device selectively causes rotation of the lead screw, rotation of the lead screw causes linear motion of the drive nut, and linear motion of the drive nut causes tensioning and untensioning of the brake cable.
According to even yet another aspect of the present invention, a method for applying a brake of a motor vehicle comprises the steps of, in combination, receiving a signal to apply the brake, starting an electric motor in response to the signal to cause a cable tensioning device to tension a brake cable, monitoring cable tension and monitoring cable travel. The method further comprises the steps of stopping the electric motor upon reaching a predetermined cable tension, and stopping the electric motor upon reaching a predetermined cable travel without reaching the predetermined cable tension.
From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology of electric parking brakes. Particularly significant in this regard is the potential the invention affords for providing a high quality, reliable, light weight, small packaged, easily assembled and disassembled, low cost assembly. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.